Liquid crystal display having improved contrast ratio and color reproduction when viewed in the lateral direction

ABSTRACT

Pluralities of pixel electrodes having openings and thin film transistors are provided on a lower panel, a common electrode having apertures is provided on an upper panel, and a liquid crystal layer vertically aligned to the two panels is located between the lower and the upper panels. The upper and the lower polarizers having the perpendicular polarizing directions are provided on the outer surfaces of the upper and the lower panels, respectively. The voltage value of a first gray representing the darkest state applied between the pixel electrode and the common electrode is within a voltage range giving a contrast ratio to be equal to or higher than 0.8 with respect to contrast ratio when the voltage applied between the pixel electrode and the common electrode is zero. In this way, the contrast ratio and the color reproduction is improved, so that the image quality of a liquid crystal display is improved.

BACKGROUND OF THE INVENTION

[0001] (a) Field of the Invention

[0002] The present invention relates to a liquid crystal display, moreparticularly, to a liquid crystal display having the improved imagequality and viewing angle.

[0003] (b) Description of the Related Art

[0004] Generally, a liquid crystal display includes an upper panelhaving a common electrode and a plurality of color filters, a lowerpanel having pluralities of thin film transistors (TFTs) and pixelelectrodes, and a liquid crystal layer between the two panels. The pixelelectrodes and the common electrode are applied with different electricpotentials to generate electric fields which vary the arrangement ofliquid crystal molecules to control the light transmittance, therebydisplaying images.

[0005] The initial arrangement of liquid crystal molecules can be, forexample, horizontally twisted or vertically aligned. A verticallyaligned structure can produce a relatively high contrast ratio and arelatively wide viewing angle. In a vertically aligned mode liquidcrystal display, longitudinal axes of liquid crystal molecules arealigned perpendicular to the upper and the lower panels in absence ofelectric field. When electric field is applied, the liquid crystalmolecules are tilted with respect to an axis normal to the panels atangles dependent on the strength of the electric field, so that thepolarization of light passing through the liquid crystal layer can bechanged. The larger the tilt angle of the liquid crystal molecules, thelarger the amount of change in polarization. If the polarization axes ofa polarizer and an analyzer opposite each other with respect to theliquid crystal layer are aligned to be perpendicular to each other, thelight which is linearly polarized after passing through the polarizerexperiences no change of the polarization in the liquid crystal layer inabsence of electric field, thereby being almost completely interceptedby the analyzer. Accordingly, the screen of the liquid crystal displaybecomes black. However, when electric field is applied, the polarizationof the linearly polarized light changes in the liquid crystal layer.Accordingly, when light reaches the analyzer, the light has apolarization component parallel to the polarization axis of theanalyzer, and thus the light out of the analyzer is visible to users.Generally, the higher the strength of the electric field applied to theliquid crystal layer, the larger the magnitude of the polarizationcomponent parallel to the polarization axis of the analyzer, and thescreen of the liquid crystal display becomes brighter.

[0006] Based on the above principle, a liquid crystal display realizesgray scale by adjusting the potential difference between the pixelelectrodes and the common electrode. Generally, the gray scale rangesfrom the first gray representing the darkest state to the sixty-fourthgray representing the brightest state.

[0007] In the meantime, the contrast ratio of a liquid crystal displaywhen viewed from its lateral sides is very poor compared with whenviewed from the front of the display. The contrast ratio is defined asthe luminance of the sixty-fourth gray divided by that of the firstgray. In addition, the color reproduction when viewed from the lateralsides is inferior to that of the front view. A liquid crystal displayhaving poor contrast ratio and inferior color reproduction cannotdisplay bright and sharp images.

SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to improve the contrastratio of a liquid crystal display when viewed from the lateral sides.

[0009] It is another object of the present invention to improve thecolor reproduction of a liquid crystal display when viewed from thelateral sides.

[0010] It is still another object of the present invention to improvethe image quality of a liquid crystal display when viewed from thelateral sides.

[0011] These and other objects are achieved by restricting the maximumvalue of the first gray voltage of a liquid crystal display to apredetermined value.

[0012] According to one aspect of the present invention, a liquidcrystal display includes a first panel having inner and outer surfacesand a second panel facing the first panel and having inner and outersurfaces. A plurality of pixel electrodes and a common electrode areprovided on one of the inner surfaces of the first and the secondpanels. A liquid crystal layer is disposed between the first and thesecond panels. Voltage value of a first gray representing the darkeststate applied between the pixel electrode and the common electrode iswithin a voltage range giving a contrast ratio to be equal to or higherthan about 0.8 with respect to contrast ratio when the voltage appliedbetween the pixel electrode and the common electrode is zero. A pair ofcrossing polarizers are disposed on the outer surfaces of the first andthe second panels and the liquid crystal layer is vertically aligned inabsence of electric field. Domain-defining member for restricting thetilt directions of molecules in the liquid crystal layer is provided inone or both of the first and the second panels. The domain-definingmember is openings in the pixel electrode or the common electrode. Inthis case, the voltage value of the first gray is equal to or lower than1.4 V. Regions divided by the openings are classified into four domainsdepending on the tilt directions of the liquid crystal molecules.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] A more complete appreciation of the invention, and many of theattendant advantages thereof, will be readily apparent as the samebecomes better understood by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings in which like reference symbols indicate the same or thesimilar components, wherein:

[0014]FIG. 1A is a sectional view of a liquid crystal display accordingto an embodiment of the present invention;

[0015]FIG. 1B is a schematic layout view illustrating the overlapbetween openings of a pixel electrode and apertures of a commonelectrode of a liquid crystal display according to the first embodimentof the present invention;

[0016]FIG. 2 is a layout view illustrating the overlap between theopenings of a pixel electrodes and apertures of a common electrode of aliquid crystal display according to the second embodiment of the presentinvention;

[0017]FIGS. 3A to 3D are graphs illustrating contrast ratios as afunction of the viewing angle θ for azimuthal angles Φ of 0°, 45°, 90°and 135°, respectively, when the applied first gray voltage is 0 volt(a) and 1.7 volts (b);

[0018]FIGS. 4A to 4D are graphs illustrating the luminance as a functionof the viewing angle θ for azimuthal angles Φ of 0°, 45°, 90° and 135°,respectively, when the applied first gray voltage is 0 volt (a) and 1.7volts (b);

[0019]FIGS. 5A and 5B show a lateral view in one polarizing directionand a front view of a liquid crystal display, respectively, when liquidcrystal molecules tilt in the other polarizing direction;

[0020]FIGS. 5C and 5D show a lateral view in the tilt direction ofliquid crystal molecules and a front view of a liquid crystal display,respectively, when the tilt direction of the liquid crystal moleculesmakes 45 degrees with both polarizing direction;

[0021]FIGS. 6A to 6D are graphs illustrating the luminance as a functionof the viewing angle θ for the various voltages of the first gray whenthe azimuthal angles Φ are 0°, 45°, 90° and 135°, respectively;

[0022]FIGS. 7A to 7D are graphs illustrating the contrast ratio as afunction of the viewing angle θ for the various voltages of the firstgray when the azimuthal angles Φ are 0°, 45°, 90° and 135°,respectively;

[0023]FIG. 8 is a graph illustrating the contrast ratio as a function ofthe first voltage for various azimuthal angles when the viewing angle θis 45°;

[0024]FIG. 9 is a graph illustrating the contrast ratio as a function ofthe viewing angle for the various voltages of the first gray withreference to the contrast ratio of 0 volt being applied;

[0025]FIGS. 10A to 10D are graphs showing the contrast ratio of thefirst embodiment of the present invention as a function of the viewingangle θ along with those of the conventional PVA (Patterned VerticalAligned), MVA (Multi-domain Vertical Aligned) and CE (coplanarelectrode) mode LCDs when the azimuthal angles Φ are 0°, 45°, 90° and135°, respectively;

[0026]FIGS. 11A to 11D are graphs showing the luminance of the firstembodiment of the present invention as a function of the viewing angle θalong with those of the conventional PVA, MVA and CE mode LCDs when theazimuthal angles Φ are 0°, 45°, 90° and 135°, respectively;

[0027]FIG. 12 is a graph illustrating the color reproductions in thefront view and the side views (θ=45°) for the first gray voltages of1.75 volts and 0.9 volts; and

[0028]FIGS. 13A and 13B are color-coordinate diagram for the first grayvoltages of 1.75 volts and 0.9 volts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The present invention now will be described more fullyhereinafter with reference to the accompanying drawings, in whichpreferred embodiments of the invention are shown. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. In the drawings, thethickness of layers and regions are exaggerated for clarity. Likenumerals refer to like elements throughout. It will be understood thatwhen an element such as a layer, region or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” another element, there are nointervening elements present.

[0030]FIG. 1A is a sectional view of a liquid crystal display accordingto an embodiment of the present invention, and FIG. 1B is a schematiclayout view illustrating the overlap between a pixel electrode andapertures of a common electrode of a liquid crystal display according tothe first embodiment of the present invention.

[0031] A liquid crystal display according to this embodiment includes alower panel 1, an upper panel 2 facing the lower panel 1, and liquidcrystal molecules 30 vertically aligned between the lower and the upperpanels 1 and 2.

[0032] A plurality of rectangular pixel electrodes 12 of transparentconductive material having openings are provided on the inner surface ofa lower substrate 10 of transparent insulating material such as glass.Each pixel electrode 12 is connected to a respective switching element11 such as a thin film transistor to be applied with image signals viathe switching element 11. The switching element 11 is connected to botha gate line (not shown) transmitting scanning signals and a data line(not shown) transmitting image signals, and turned on/off responsive tothe scanning signal to transmit the image signals to the respectivepixel electrode 12. In addition, a lower polarizer 14 is attached to theouter surface of the lower substrate 10. In a reflective type liquidcrystal display, the lower substrate 10 and the pixel electrodes 12 maybe made of opaque material. In this case, the lower polarizer 14 is notrequired.

[0033] A black matrix 21 for preventing light leakage, a plurality ofcolor filters 22 and a common electrode 23 of transparent conductivematerial such as ITO (Indium-Tin Oxide) or IZO (Indium-Zinc Oxide)having apertures are provided on the inner surface of an upper substrate20 of transparent insulating material such as glass. The black matrix 21or the color filters 22 may be provided on the lower substrate 10. Inaddition, an upper polarizer 24 is attached to the outer surface of theupper substrate 20.

[0034] The liquid crystal display according to this embodiment is in thenormally black mode, where the polarizing directions of the lower andthe upper polarizers 14 and 24 are aligned perpendicular to each other,and the screen becomes dark as the electric field generated by the pixelelectrode and the common electrode to be applied to the liquid crystalmolecules is reduced.

[0035] In this liquid crystal display, the apertures and the openings ofthe common electrode 23 and the pixel electrodes 12 are used forrestricting the tilt directions of the liquid crystal molecules. Theshapes and arrangement of the openings and the apertures according tothe present invention will be described in detail.

[0036] As shown in FIG. 1B, there are provided three openings 122, 121and 123 in the rectangular pixel electrode 12, which are arranged in alongitudinal direction. A middle opening 121 extends in a transversedirection from the right side of the pixel electrode 12 toward the leftside. The corners of the pixel electrode 12 near the inlet of the middleopening 121 are chamfered at a smooth angle to be curved. Upper andlower openings 122 and 123 are provided in upper and lower portions ofthe pixel electrode 12 opposed to each other with respect to the middleopening 121. Each of the upper and the lower openings 122 and 123 startsat a proximal corner of the pixel electrode 12, away from the middleopening 121, and continues toward the middle opening 121 in a diagonaldirection. In this embodiment, the upper and the lower openings 122 and123 are symmetrical with respect to the middle opening 121.

[0037] The common electrode 23 includes three apertures 220, 210 and 230arranged in the longitudinal direction. A middle aperture 210 has a stem211 extending from the left side in the transverse direction, upper andlower oblique branches 212 and 214 extending from the end of the stem211 obliquely upward and downward, respectively, and upper and lowerlongitudinal branches 213 and 215 extending from the ends of the upperand the lower oblique branches 212 and 214, respectively. The upperbranch 212 is nearly perpendicular to the lower branch 214. An upperaperture 220 has a middle portion 221 extending parallel to the upperoblique branch 212, and transverse and longitudinal portion 222 and 223extending from upper and lower ends of the middle portion 221 in thetransverse and the longitudinal directions, respectively. The loweraperture 230 and the upper aperture 220 are symmetrically arranged withrespect to middle aperture 210. That is, a middle portion 231 of thelower aperture 230 is arranged parallel to the lower oblique branch 214of the middle aperture 210, and longitudinal and transverse portion 233and 232 extends from the upper and the lower ends of the middle portion231 in the longitudinal and the transverse directions, respectively.Such arrangement of the apertures 210, 220 and 230 is providedrepeatedly on the common electrode 23.

[0038] The openings 121, 122 and 123 of the pixel electrode 12 and theapertures 210, 220 and 230 of the common electrode 23 divide the pixelelectrode 12 into a plurality of areas to define domains. The openings121, 122 and 123 of the pixel electrode 12 and the apertures 210, 220and 230 of the common electrode 23 are alternately arranged. Theopenings 122 and 123 are parallel to the middle portions 221 and 231 aswell as the oblique branches 212 and 214, respectively. These obliqueopenings 122 and 123, and portions 221 and 231, and branches 212 and 214of the apertures 210, 220 and 230 form long edges of the areas, whilethe opening 121, the portions 222, 223, 232 and 233, the stem 211 andthe branches 213 and 215 in the longitudinal or transverse directionsform short edges of the areas.

[0039] The polarizing directions of the upper and the lower polarizers14 and 24 are aligned in the transverse and the longitudinal directions,respectively, or vice versa.

[0040] In this structure, since most of the liquid crystal moleculesapplied with electric fields tend to tilt in the direction perpendicularto the long edges, there are four different average tilt directions toform four domains which generate wide viewing angle, and the number ofthe liquid crystal molecules tilting in the polarizing direction of thepolarizers 14 and 24 decreases to reduce texture. In addition, since thearrangement of the liquid crystal molecules may be completed nearlyimmediately, the response time is very short.

[0041] The second embodiment of the present invention will be describedwith the accompanying drawings.

[0042]FIG. 2 is a layout view illustrating openings of a pixel electrodeand apertures of a common electrode of a liquid crystal displayaccording to the second embodiment of the present invention. Thestructure of the second embodiment is similar to that of the firstembodiment except for the shapes of the openings and apertures.

[0043] The pixel electrode 12 includes a longitudinal opening 111 andthree transverse openings 120, 130 and 140 arranged along thelongitudinal direction. The longitudinal opening 111 extends downwardfrom the upper edge of the pixel electrode 12, and divides the upperportion of the pixel electrode 12 into two partitions arranged in thetransverse direction. The transverse openings 120, 130 and 140 extendleftward from the right edge of the pixel electrode 12, and divide thelower portion of the pixel electrode 12 into four partitions arrangedalong the longitudinal direction.

[0044] The common electrode 23 includes an upper aperture 210 having twolongitudinal portions 212 and 214 and a transverse portion 216 connectedthereto, and three lower transverse apertures 230, 240 and 250, and theupper and the lower apertures 210, 230, 240 and 250 are laterallyarranged along the longitudinal direction.

[0045] Each of the two longitudinal portions 212 and 214 divides therespective upper partition into two areas, thereby forming four upperareas. The upper two 230 and 240 of the lower apertures 230, 240 and 250divide the middle two of the lower partitions of the pixel electrodes12, and the transverse portion 216 of the upper aperture 210 and thelowest aperture 250 form the upper and the lower edges of the lowerportion of the pixel electrode 12.

[0046] The voltage of the first gray representing the darkest state in aliquid crystal display is confined in a range and this will be describedin detail.

[0047] According to a preferred embodiment of the present invention, thevoltage of the first gray is determined in a voltage range which givesthe contrast ratio to be equal to or larger than about 0.8 in allviewing directions when compared to contrast ratio when applying 0 volt.The voltage range depends on the type of the liquid crystal panel. Inthe LCD according to the embodiments wherein the liquid crystalmolecules are arranged vertical to the upper and the lower panels andthe openings and the apertures are provided on both the pixel electrodeand the common electrode, the voltage range of the first gray is within0 volt to 1.4 volts. The reason for the limitation of the voltage rangeof the first gray will be described below.

[0048] Advantageously, lateral contrast ratio and lateral colorreproduction of the liquid crystal display are largely improved.

[0049]FIGS. 3A to 3D are graphs illustrating contrast ratios as afunction of the viewing angle θ for azimuthal angles Φ of 0°, 45°, 90°and 135°, respectively. The two curves are those when the applied firstgray voltage is 0 volt (a) and 1.7 volts (b).

[0050] The voltage of 1.7 volts was chosen because the voltage of 1.7volts is less than the threshold voltage where the transmittance startsincreasing in the V-T (voltage-transmittance) curve measured in front ofa liquid crystal display and because this voltage gives suitable voltagegaps between this voltage and the successive second and third grayvoltages.

[0051] As shown in FIGS. 3A to 3D, it is apparent that the contrastratio of 0 volt is better than that of 1.7 volts in all viewing angles.

[0052]FIGS. 4A to 4D are graphs illustrating the luminance as a functionof the viewing angle θ for azimuthal angles Φ of 0°, 45°, 90° and 135°,respectively. The two curves are those when the applied first grayvoltage is 0 volt (a) and 1.7 volts (b).

[0053] As shown in FIGS. 4A to 4D, it is apparent that the luminance of1.7 volts is higher than that of 0 volt in all viewing angles. Highluminance in the first gray representing the darkest state means highlight leakage in the black state.

[0054] For azimuthal angles of 0° and 90°, the luminance curve of 1.7volts exhibits high peaks near ±50° while that of 0 volt showing nopeak. For azimuthal angles of 45° and 135°, both the luminance curves of0 volt and 1.7 volts show high peaks, but the luminance of 1.7 volts isstill larger than that of 0 volt. This high luminance of 1.7 volts mayresult in high contrast.

[0055]FIGS. 5A to 5D show liquid crystal molecules applied with avoltage of 1.7 volts. FIGS. 5A and 5B are lateral views in onepolarizing direction and a front view of a liquid crystal display,respectively, when liquid crystal molecules tilt in the other polarizingdirection. FIGS. 5C and 5D are lateral views in the tilt direction ofliquid crystal molecules and a front view of a liquid crystal display,respectively, when the tilt direction of the liquid crystal moleculesmakes 45 degrees with both polarizing direction.

[0056] Although the threshold voltage of a liquid crystal display ishigher than 1.7 volts, the liquid crystal molecules are minutely moved.The retardation in the lateral view is large compared with that in thefront view, as shown in FIGS. 5A to 5D. Accordingly, the brightness inthe front view is low while that in the lateral view is relatively high.In addition, the retardation variation in the lateral view when the tiltdirection makes 45 degrees with the polarizing directions is smallerthan that when the tilt direction is parallel to the polarizingdirection, as shown in FIGS. 5A and 5C, and this causes small contrastvariation.

[0057]FIGS. 6A to 6D are graphs illustrating the luminance as a functionof the viewing angle θ for various voltages of the first gray when theazimuthal angles Φ are 0°, 45°, 90° and 135°, respectively, and FIGS. 7Ato 7D are graphs illustrating the contrast ratio as function of theviewing angle θ for various voltages of the first gray when azimuthalangles Φ are 0°, 45°, 90° and 135°, respectively.

[0058] As the first gray voltage decreases, the luminance decreaseswhile the contrast ratio increases. The contrast ratio curve of theapplied voltage of 0.8 volts shows the same as that of zero voltage.

[0059]FIG. 8 is a graph illustrating the contrast ratio as a function ofthe applied voltage for several azimuthal angles when the viewing angleθ is 45°. As shown in FIG. 8, contrast ratio increases as the appliedvoltage decreases for all azimuthal angles.

[0060]FIG. 9 is a graph illustrating the contrast ratio of a PVA(Patterned Vertically Aligned) LCD in the polarizing direction as afunction of the viewing angle for various applied voltages withreference to that of zero volt.

[0061] As shown in FIG. 9, the variation of the contrast ratio dependingon the viewing angle becomes larger as the applied voltage becomeshigher. It is understood that the applied voltage equal to or smallerthan 1.4 volts gives the contrast ratio equal to or higher than 0.8 inall viewing directions. However, this value may be varied depending onthe type of LCD or the kind of liquid crystal material.

[0062] The light leakage is larger in the diagonal direction than in thepolarizing direction even when applying 0 volt as the first grayvoltage, and this may be compensated by adjusting the retardation valueof a phase compensation film or changing a cell gap.

[0063] In order to review the effect of the present invention, thecontrast ratio and the luminance of the white color of an LCD accordingto the present invention were compared with those of conventional liquidcrystal displays.

[0064]FIGS. 10A to 10D are graphs showing contrast ratio as a functionof the viewing angle θ for an LCD according to the first embodiment ofthe present invention, and conventional PVA, MVA (Multi-domainVertically Aligned) and CE (Coplanar Electrode) mode LCDs, when theazimuthal angles Φ are 0°, 45°, 90° and 135°, respectively.

[0065]FIGS. 11A to 11D are graphs showing the luminance as a function ofthe viewing angle θ for an LCD according to the first embodiment of thepresent invention, and conventional PVA, MVA and CE mode LCDs when theazimuthal angles Φ are 0°, 45°, 90° and 135°, respectively.

[0066] A PVA mode LCD is a vertically aligned mode LCD having openingsas domain-defining members, an MVA mode LCD is also a vertically alignedmode LCD but having projections as domain-defining members, and a CEmode LCD has pixel electrodes and a common electrode provided in thesame panel.

[0067] As shown in FIGS. 10A to 10D, the contrast ratio of the liquidcrystal display according to the embodiment of the present invention issuperior in all viewing angles except for the case of the azimuthalangle of 45 degrees shown in FIG. 10B.

[0068] As shown in FIGS. 11A to 11D, the luminance of the white color ofthe liquid crystal display according to the embodiment of the presentinvention is superior to the MVA mode and is similar or slightlysuperior to the CE mode.

[0069] Next, the color reproduction will be described.

[0070]FIG. 12 and Table 1 illustrate the color reproductions in thefront view and the lateral views (θ=45°) when the applied voltage is1.75 volts and 0.9 volts. TABLE 1 First Gray Voltage Front Left 45°Right 45° Top 45° Bottom 45° 1.75 V 51.3 49.2 48.2 42.0 42.8  0.9 V 51.853.8 52.9 54.1 53.5

[0071] As shown in Table 1 and FIG. 12, the color reproduction of 1.75volts is similar to that of 0.9 vots in the front view, while severelydeteriorated in the lateral view. This can be understood in the samemanner as the decrease of the contrast ratio and the increase ofluminance in the lateral view, as described above. For example, whenblue color is intended to display, the red and the green pixels areapplied with the first gray voltage to be dark and only the blue pixelis applied with higher gray voltage to be brightened. However, leakedlight in the red and the green pixels applied with the first grayvoltage is mixed to distort the display of pure blue color.

[0072]FIGS. 13A and 13B are color-coordinate graphs when the first grayvoltage is 1.75 volts and 0.9 volts, respectively.

[0073] As described above, when displaying the blue color, the lightleakages in the red and the green pixels make color-coordinate to movetoward the white color. In this way, when displaying the red or thegreen color, the light leakages in the other color pixels also makecolor-coordinate to move toward the white color, thereby diminishing thesize of a triangle connecting the red, the green and the blue colors.The decreases of the size of the triangle connecting the red, the greenand the blue color means that displayable color range is small, therebycolor reproduction is deteriorated.

[0074] Accordingly, to improve color reproduction, the first grayvoltage should be smaller than a value as taught by the presentinvention.

[0075] As described above, the contrast ratio and the color reproductioncan be improved by lowering the first gray voltage, so that the imagequality of a liquid crystal display is improved.

[0076] While the present invention has been described in detail withreference to the preferred embodiments, those skilled in the art willappreciate that various modifications and substitutions can be madethereto without departing from the spirit and scope of the presentinvention as set forth in the appended claims.

What is claimed is:
 1. A liquid crystal display comprising: a firstpanel having inner and outer surfaces; a second panel facing the firstpanel and having inner and outer surfaces; a pixel electrode provided onthe inner surface of the first panel; a common electrode provided on theinner surface of the second panel; and a liquid crystal layer betweenthe first and the second panels, wherein voltage value of a first grayrepresenting the darkest state applied between the pixel electrode andthe common electrode is within a voltage range giving a contrast ratioto be equal to or higher than about 0.8 with respect to contrast ratiowhen the voltage applied between the pixel electrode and the commonelectrode is zero.
 2. The liquid crystal display of claim 1 furthercomprising a first and second polarizers disposed on respective outersurfaces of the first and the second panels.
 3. The liquid crystaldisplay of claim 2, wherein the liquid crystal layer is verticallyaligned in absence of electric field.
 4. The liquid crystal display ofclaim 3 further comprising domain-defining member for restricting thetilt directions of molecules in the liquid crystal layer, provided inone or both of the first and the second panels.
 5. The liquid crystaldisplay of claim 4, wherein the domain-defining member is openings inthe pixel electrode or the common electrode.
 6. The liquid crystaldisplay of claim 5, wherein the voltage value of the first gray is equalto or lower than 1.4 V.
 7. The liquid crystal display of claim 6,wherein the openings are provided in both the pixel electrode and thecommon electrode.
 8. The liquid crystal display of claim 7, whereinregions divided by the openings are classified into four domainsdepending on the tilt directions of the liquid crystal molecules.
 9. Aliquid crystal display comprising: a first and second panel, each havinginner and outer surfaces, with inner surfaces facing each other; acommon electrode disposed on the inner surface of the first panel and acommon electrode disposed on the inner surface of the second panel; anda liquid crystal layer having crystal molecules disposed between thefirst and second panels, wherein a domain defining member is formed inone of the common electrode and the pixel electrode for restricting thetilt directions of the crystal molecules.
 10. The display according toclaim 9, wherein the domain defining member includes an upper opening,middle opening and a lower opening arranged laterally along alongitudinal direction, the upper and lower openings being symmetricallyspaced with respect to the middle opening.
 11. The display according toclaim 10, wherein each of the upper and lower openings includes a slantportion which slants toward the middle opening.
 12. The displayaccording to claim 10, wherein the domain defining member furtherincludes upper, lower, and middle apertures, the upper and lowerapertures having the same shape and are disposed symmetrically about themiddle aperture.
 13. The display according to claim 12, wherein each ofthe apertures includes at least one slant portion, the slant portion inthe upper and lower apertures slanting in a parallel direction withrespect to one of two slants in the middle aperture.
 14. The displayaccording to claim 9, wherein the domain defining member includes aplurality of openings arranged laterally along a longitudinal direction,with at least one opening disposed in a direction transverse to thelongitudinal direction.